On Sat, 26 Jan 2013 13:11:11 -0500, bitrex wrote:

On 1/26/2013 12:18 PM, Jim Thompson wrote:
What are these nodes?

http://tinyurl.com/bjxndpg

...Jim Thompson


I lurk here mostly, but I don't understand the big deal over this
circuit. Isn't it just a poor man's TIA? Input current against R5
creates current in the output -Iin*R5/R4 so (neglecting the small
current contribution from Iin) Vo/Iin = -(R5*(R3+R4))/R4?

James assumed that the signal source was a voltage, whose source impedance,
including the coupling cap C2, was far lower than the 220K bias resistor, so the
thing runs open-loop with a voltage gain of hundreds. The whole point of
bootstrapping was to increase the overall voltage gain. The feedback is just to
set the DC operating point, not to limit the gain or to make a TIA. As James
said, if AC feedback were a concern, add a bypass cap in the feedback path so
that it isn't.

The true poor man's TIA is a single resistor to ground.






--

John Larkin Highland Technology Inc
www.highlandtechnology.com jlarkin at highlandtechnology dot com

Precision electronic instrumentation
Picosecond-resolution Digital Delay and Pulse generators
Custom timing and laser controllers
Photonics and fiberoptic TTL data links
VME analog, thermocouple, LVDT, synchro, tachometer
Multichannel arbitrary waveform generators